The present invention relates to electromagnetic shielding devices. More particularly, the present invention relates to an electromagnetic shielding device for shielding two adjacent, relatively movable members having opposed surfaces with a space therebetween.
It has been known that electronic shielding of fixed or movable joints in shielded structures such as test rooms and enclosures for radio transmitters, radio receivers, computers and other equipment is highly desirable. Such structures often have movable members primarily at doors, access panels, drawers and the like. It is highly desirable to shield these joints effectively with conductive surfaces that permit dissipation of electrical charges and thereby isolate the charge within the structure.
Various arrangements for effecting the seal have been proposed. However, many of the prior proposals have been found not to provide proper attenuation due, in part, to poor electrical contact between the opposed surfaces. This problem is particularly acute with surfaces in which the direction of final closure is generally parallel to the surfaces, i.e., doors. The forces transmitted to the shielding arrangement during such a sliding, parallel closing movement are often detrimental to the structure of the known shielding arrangements thereby causing a loss in proper electrical contact between the surfaces. For example, the shielding arrangement may be insufficiently secured to the surface to ensure proper contact therewith particularly with repeated openings and closings of the relatively movable members.
One prior shielding arrangement is disclosed in U.S. Pat. No. 3,504,095 issued Mar. 31, 1970 to Roberson et al. In a preferred embodiment, the Roberson patent discloses an electromagnetic gasket including a longitudinal bearing portion and a curved bearing portion. A plurality of notches divide the curved bearing portion into a row of integral fingers along the entire length of the gasket. The gasket is secured to one of a pair of opposed surfaces by an adhesive along the lower portion of the longitudinal bearing portion.
Other types of electromagnetic shielding arrangements including longitudinal or circular strips arranged upon one of two opposed surfaces are disclosed in U.S. Pat. Nos. 2,825,042 issued Feb. 25, 1958 to Tollefson et al; 2,844,644 issued July 22, 1958 to Soule Jr.; 3,277,230 issued Oct. 4, 1966 to Stickney et al; and 3,904,810 issued Sept. 9, 1975 to Kraus.
Another known joint seal for electromagnetic wave shielding includes spring strips of angular cross section providing an electromagnetic seal between a pair of movable members. The spring strips are confined in opposing pairs under a clamp which is attached by a screw to one of the movable members. An arrangement of this type is disclosed in U.S. Pat. No. 3,962,550 issued June 8, 1976 to Kaiserswerth.
It is an object of the present invention to provide an electromagnetic shielding device which is effective to obtain and retain good electrical contact between surfaces on two relatively movable members even after repeated openings and closings of the members.
It is a further object of the present invention to provide an electromagnetic shielding device which is useful on a wide variety of different types of both surface textures and materials and different types of relative movements between the movable members. Still a further object of the present invention is to provide an electromagnetic shielding device which is not prone to wear with repeated movements of the relatively movable members.
Yet another object of the present invention is to provide an electromagnetic shielding device that is positively retained upon a surface. Further, it is an object of the present invention to provide an electromagnetic shielding device which is relatively inexpensive to manufacture and relatively easy to install.
A still further object of the present invention is to provide an effective arrangement for shielding two opposed surfaces on relatively movable members having a space therebetween.
These objects and others are accomplished by an electromagnetic shielding device and an arrangement for shielding two adjacent, relatively movable members in accordance with the present invention. The shielding device includes a resilient cap portion having a solid center portion and a plurality of segments extending radially outwardly therefrom. The device further includes a retaining member for retaining the cap portion on a surface.
In a preferred embodiment, the shielding device includes radially outwardly extending segments with resilient tongues extending radially inwardly from an outer end of each of the segments. A first portion of the retaining member is adapted to be received within an annular space defined between the segments and the resilient tongues. The first portion of the retaining member preferably comprises a disk while the retaining member includes a second portion adapted to be secured to the surface. Further in the preferred embodiment, the cap portion includes an odd number of segments such that mechanical stresses on the cap portion when initially engaged in sliding contact between the two surfaces is minimized.
In accordance with a further aspect of the present invention, the arrangement for electromagnetic shielding of two adjacent relatively movable members having opposed surfaces with a space therebetween includes a plurality of individual spaced apart shielding elements arranged on one of the surfaces. Each element comprises a resilient cap portion and an arrangement for retaining the cap portion on the one surface. A height of the cap portion from the surface in a free state is greater than the distance of the space between the opposed surfaces such that the cap portion is compressed to fit within the space upon movement of the members toward one another. It is further preferred that the spacing between adjacent ones of the plurality of shielding elements is less than one half of the wavelength of the highest frequency to be shielded.